Flat tube heat exchanger

ABSTRACT

The invention relates to a flat tube heat exchanger, in particular to a high-temperature flat tube heat exchanger for gaseous media, comprising a closed housing (5) having a tube bundle space (50) and a tube bundle, arranged in the tube bundle space (50) of the housing (5), comprising multiple flat tubes (2), there being arranged, in the flat tubes (2) and in the tube bundle space (50) between the flat tubes (2), corrugated strips (3, 6) having peaks (30, 60) and troughs (31, 61) extending in the longitudinal direction of the flat tubes (2), wherein the peaks (30, 60) and troughs (31, 61) respectively bear internally and externally against flat sides (200) of the flat tubes (2), and wherein there is provided a device for externally applying a surface pressure to the housing (5), at least in the region of the tube bundle space (50), this pressure being higher than a pressure (p1, p2) of the media guided in the flat tubes (2) or around the flat tubes (2).

FIELD OF APPLICATION AND PRIOR ART

The invention relates to a flat-tube heat exchanger, in particular a high-temperature flat-tube heat exchanger for gaseous media.

Flat-tube heat exchangers are generally known. By way of example, EP 2 584 301 A1 describes a high-temperature flat-tube heat exchanger for gaseous media, comprising a closed housing having, on two mutually opposite sides, two tube sheets which partition an input-side collecting space, a tube bundle space and an output-side collecting space in the housing, and comprising a tube bundle which consists, at least predominantly, of rectilinear flat tubes with round or polygonal ends, wherein a tube bundle space comprises three zones, namely two cross-flow zones formed in the region of tube bundle space connections and one longitudinal flow zone formed between these cross-flow zones. The flat-tube heat exchanger described in said document can be employed in the case of high temperature spread and frequent temperature change without the risk of stress cracks. Such flat-tube heat exchangers have repeatedly proven to be effective in particular at gas inlet temperatures of up to 1100° C.

The efficiency of a flat-tube heat exchanger is, inter alia, dependent on the number of flat tubes used. Typically, use of a flat-tube heat exchanger involves an efficiency of about 75%. In the case of a conventional flat-tube heat exchanger, in order to further increase the efficiency from about 75% to about 90% with the same throughput, the number of flat tubes has to be approximately tripled. This is generally not possible in an economically viable manner.

OBJECT AND ACHIEVEMENT

It is the object of the invention to provide a flat-tube heat exchanger having an improved efficiency.

This object is achieved by means of a flat-tube heat exchanger, in particular for gaseous media, comprising a closed housing having a tube bundle space and a tube bundle which is arranged in the tube bundle space of the housing and which comprises a plurality of flat tubes, wherein corrugated bands having troughs and peaks extending in a longitudinal direction of the flat tubes are arranged in the flat tubes and in the tube bundle space between the flat tubes, wherein the troughs and peaks bear internally or externally against flat sides of the flat tubes, and wherein provision is made of an apparatus for externally applying a surface pressure to the housing, at least in the region of the tube bundle space, said surface pressure being higher, in particular about 1 bar to about 4 bar higher, than a pressure of the media guided in the flat tubes or around the flat tubes.

By means of the corrugated bands, a surface for heat transfer from or to the medium guided in the flat tubes, also referred to as a transfer surface, can be more than doubled. At the same time, a hydraulic diameter for a flow through the flat tubes and around the flat tubes is reduced, with the result that a heat transfer coefficient, in counter-flow operation, is increased in an inversely proportional manner.

By means of the apparatus for applying a surface pressure to the housing, deformation of the flat tubes, for example owing to a temperature or a pressure of the medium guided therein, which may lead to contact losses is reliably prevented. The flat-tube heat exchanger is thus suitable for being operated both with high pressure differences between the media guided in the flat tubes and around the flat tubes and with high temperature fluctuations, for example during start-up and shutdown.

In conjunction with the application, the expression “in the flat tubes” should not be interpreted as “in all the flat tubes”. Rather, both configurations in which only some of the flat tubes comprise corrugated bands and configurations in which all the flat tubes comprise corrugated bands are conceivable. Similarly, in conjunction with the application, the words “a” and “an” are used only as indefinite articles and should not be interpreted as being indicative of number.

The housing usually comprises two collecting spaces which allow a first medium to flow into the flat tubes and the first medium to flow out of the flat tubes.

In the case of a tube bundle which is flowed through in one direction, the collecting spaces are arranged at opposite ends of the tube bundle space. In order to supply a second medium to the tube bundle space and to discharge it therefrom, tube bundle space connections are provided at the ends lying opposite one another as viewed in a flow direction, or on sides of the housing.

The term flat tubes refers to tubes which are flat at least on a central portion lying between two ends, i.e. which have two mutually opposite flat sides and two narrow sides connecting the flat sides. In one configuration, the central portions of the flat tubes have a stadium-shaped cross section with two mutually parallel, planar flat sides and two narrow sides which connect the flat sides and which are curved, for example curved in a semicircular manner. In this case, use can be made of a corrugated band which has a constant height and the troughs and peaks of which touch the flat sides. In configurations, the ends of the flat tubes, said ends lying opposite one another in the longitudinal direction, have a cross section, which differs from the central portion, for a connection to the collecting spaces, in particular a circular cross section, a polygonal cross section or the like.

In one configuration, the flat-tube heat exchanger is constructed in the form of a rectangular arrangement with a cuboid tube bundle space and with a plurality of flat tubes arranged in rows and columns. In another configuration, the flat-tube heat exchanger is constructed in the form of a round arrangement with a cylindrical tube bundle space having a circular or a polygonal cross section. In one configuration, in a round arrangement, the heat exchanger is constructed in the form of a ring heat exchanger, wherein the flat tubes are arranged along a plurality of concentric circular rings having different diameters.

In one configuration, the corrugated bands have a sinusoidal, triangular or sawtooth wave shape. These wave shapes have in common the fact that the peaks and troughs bear, in the ideal case linearly, against the flat sides merely along a narrow strip extending in the longitudinal direction. As a result, accumulations of material, which have a negative influence on heat transfer, are avoided or at least minimized at contact points. A person skilled in the art can select a wave shape in a suitable manner depending on the application, in order to obtain a desired increase in a transfer surface. It is also possible in this case to provide a standard module of a flat-tube heat exchanger, in which case flat-tube heat exchangers having differently dimensioned transfer surfaces are provided through selection of suitable corrugated bands.

Depending on the material and wall thickness of the corrugated bands, the corrugated bands simultaneously also serve as support means against deformation of the flat tubes owing to a negative pressure of the medium guided in the flat tubes in relation to the medium guided around the flat tubes. In configurations of the flat-tube heat exchanger, a width of the corrugated bands is at least equal to a width of the flat sides of the flat tubes.

A height of the corrugated bands arranged in the flat tubes is approximately equal to a height of the flat tubes, wherein the corrugated bands and the flat tubes have, for example, a height of about 2 to about 4 mm. In one configuration, provision is made for the flat tubes to be expanded by means of pressure and/or temperature for insertion of the corrugated bands, wherein after the pressure and/or the temperature has been canceled, the corrugated bands bear against the flat sides of the flat tubes. In one configuration, a height of the corrugated bands arranged between the flat tubes is approximately equal to a spacing between adjacent flat tubes, with the result that the peaks and troughs of these corrugated bands bear against the flat sides of adjacent flat tubes.

In one configuration, the peaks and troughs bear freely against flat sides of the flat tubes, i.e. the corrugated bands are not welded or soldered to the flat tubes or connected thereto with a material bond in some other way. As a result, complex and thus expensive welded connections are in particular omitted. In addition, it is possible to provide corrugated bands or flat tubes from a non-weldable or non-solderable material. Since provision is made according to the invention of an apparatus for externally applying a surface pressure to the housing, at least in the region of the tube bundle space, said surface pressure being higher than a pressure of the media guided in the flat tubes or around the flat tubes, contacting of the corrugated bands with the flat tubes is ensured during operation even without a materially bonded connection of the corrugated bands to the flat tubes.

In one configuration, the apparatus comprises a casing housing which accommodates the housing, wherein the casing housing surrounds the housing, at least in the region of the tube bundle space, with a spacing so as to leave a pressure space. This casing housing is shaped, and designed, in such a way that a fluid can be accommodated in the pressure space, the pressure of said fluid being higher, in particular about 1 bar to about 4 bar higher, than a pressure of the media in the interior of the housing. In this case, a person skilled in the art can design the casing housing in a suitable manner depending on the application. In one configuration, thermal insulation is provided around the housing in order to avoid, or at least reduce, the heating of a fluid present in the pressure space between the housing and the casing housing.

In one configuration, the casing housing is in the form of a pressure vessel having a connection for media supply and/or media discharge, wherein a pressure in the pressure vessel can be regulated by media supply and/or media discharge. In conjunction with the application, the term pressure vessel refers to a closed vessel for accommodating a pressurized fluid at least without substantial deformation, if any, wherein a pressure inside the pressure vessel is above the ambient pressure.

In an alternative configuration, the apparatus comprises a pair of bars and/or plates having two flexurally rigid bars and/or plates which are movable relative to one another and which are connected by means of tie rods, wherein at least one portion of the housing is arranged between the bars and/or plates of the pair of bars and/or plates. The bars or plates of a pair of bars or of a pair of plates, respectively, are connected by means of tie rods and can be braced with one another with a defined force by means of a suitable device. As has already been mentioned above, in conjunction with the application, the words “a” and “an” are used only as indefinite articles and should not be interpreted as being indicative of number. This apparatus may in particular comprise more than one pair of bars and/or plates. A person skilled in the art can select the number of pairs of bars and/or plates in a suitable manner depending on the application. As a result, an inexpensive apparatus for applying a surface pressure to the housing is provided, said apparatus being expedient in particular for fields of use in which no or only a moderate overpressure is present in and around the flat tubes. By way of example, a flat-tube heat exchanger comprising such an apparatus may be employed in thermal post-combustion of contaminated air or offgas.

In one configuration, the pair of bars and/or plates acts directly on the housing. In an advantageous configuration, the apparatus further comprises a casing housing, wherein the casing housing surrounds the housing, at least in the region of the tube bundle space, with a spacing. The force applied to the casing housing by the pair of bars and/or plates is transmitted to the housing. In one configuration, this is effected by means of a non-compressible fluid present in the casing housing. In advantageous configurations, pressure rams for force transmission are arranged between the casing housing and the housing. The casing housing can be externally loaded by means of the pair of bars and/or plates, the loading being transmitted to the housing by means of the pressure rams. In one configuration, thermal insulation is additionally provided between the casing housing and the housing.

In one configuration, the corrugated bands are at least partially coated with a material acting as a catalyst. Such a coating is advantageous, for example, when using the flat-tube heat exchanger in a reactor for endothermic processes, for example for reforming hydrocarbons, or for exothermic processes, for example for synthesizing synthetic fuels. Particularly if the corrugated bands bear freely against the flat tubes, a coating is possible without limitations regarding weldability. In configurations of the flat-tube heat exchanger, exclusively those corrugated bands arranged in the flat tubes or exclusively those corrugated bands arranged outside the flat tubes are coated. In other configurations, the corrugated bands arranged in the flat tubes and the corrugated bands arranged outside the flat tubes have different coatings.

In one configuration, exactly one corrugated band is provided in a flat tube, wherein a length of the corrugated band in the longitudinal direction of the flat tube is smaller than or equal to a length of the central portion of the flat tube. In this case, a flow through the flat tube with the corrugated band is laminar, provided that no further measures are taken.

In an alternative configuration, as viewed in the longitudinal direction, in each case at least two corrugated bands are arranged so as to run oppositely in the flat tubes. An oppositely running arrangement refers in this case to an arrangement phase-shifted by 180°, such that peaks and troughs of a corrugated band are arranged in alignment with troughs and peaks, respectively, of an adjacent corrugated band. As a result of this measure, swirling of the flow through the flat tube for improved heat transfer is achieved.

In this case, in one configuration, transverse ribs are arranged between two adjacent corrugated bands. Further swirling is achieved by means of the transverse ribs. In one configuration, the corrugated bands and the transverse ribs are connected to one another. In other configurations, the corrugated bands bear freely against the transverse ribs.

In one configuration, the flat tubes are each composed of at least two flat tube pieces which each extend in the longitudinal direction. In one configuration, the flat tube pieces are produced from a tube which has a short portion of circular cross section and smaller diameter and a portion of circular cross section and larger diameter. The portion of larger diameter can be pressed flat in a forming process, for example a rolling process, in particular between cylindrical rollers. The corrugated bands can then be inserted into the formed portions, and two flat tube pieces which are arranged in a mirror-symmetrical manner can be connected, in particular welded, to one another. In this case, it is possible, in particular for a use with a large temperature spread of, for example, up to 1000° C., for the flat tube to be composed of flat tube pieces made of various materials.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and aspects of the invention emerge from the claims and from the following description of exemplary embodiments of the invention, which are explained below on the basis of the schematic figures. In the drawings:

FIG. 1 shows a longitudinal section of a flat tube for a flat-tube heat exchanger, wherein a corrugated band having peaks and troughs extending in the longitudinal direction of the flat tube is arranged in the flat tube,

FIG. 2 shows the flat tube according to FIG. 1 in cross section along section line II-II according to FIG. 1 ,

FIG. 3 shows the flat tube according to FIG. 1 in cross section along section line III-III according to FIG. 1 ,

FIG. 4 shows a longitudinal section of a tube bundle space of a flat-tube heat exchanger having a plurality of flat tubes according to FIG. 1 ,

FIG. 5 shows a plan view of the tube bundle space according to FIG. 4 ,

FIG. 6 shows the tube bundle space according to FIG. 4 in cross section along section line VI-VI according to FIG. 4 ,

FIG. 7 shows a longitudinal section of a first configuration of a flat-tube heat exchanger having a plurality of flat tubes, wherein a housing of the flat-tube heat exchanger is surrounded by a casing housing in the form of a pressure vessel,

FIG. 8 shows the flat-tube heat exchanger according to FIG. 7 in cross section along section line VIII-VIII according to FIG. 7 ,

FIG. 9 shows a longitudinal section of a second configuration of a flat-tube heat exchanger having a plurality of flat tubes, wherein a housing of the flat-tube heat exchanger is surrounded by a casing housing to which a surface pressure is applied by means of a plurality of pairs of bars,

FIG. 10 shows a flat-tube heat exchanger according to FIG. 9 in cross section along section line X-X according to FIG. 9 ,

FIG. 11 shows a perspective illustration of an alternative arrangement of corrugated bands, and

FIG. 12 shows a cross section of a flat tube with the arrangement of corrugated bands according to FIG. 11 .

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following description of exemplary embodiments of the invention, the same reference designations are used for the same or similar components.

FIGS. 1 to 3 show a flat tube 2 for a flat-tube heat exchanger 1 (cf. FIGS. 7 to 10 ), which is not illustrated in FIGS. 1 to 3 , in longitudinal section and in two cross sections along section lines II-II and according to FIG. 1 .

The flat tube 2 has two ends 21, 22 and a central portion 20 lying between the two ends 21, 22. A cross section of the central portion 20 has a stadium shape with two mutually parallel planar flat sides 200 and two narrow sides 201 which connect the flat sides 200 and which are curved, for example curved in a semicircular manner in the exemplary embodiment illustrated. The ends 21, 22 have a cross section, which differs from the central portion 20, for a connection to collecting spaces of a housing of the flat-tube heat exchanger 1 (not illustrated), for example a circular cross section.

Two corrugated bands 3 having peaks 30 and troughs 31 (cf. FIGS. 2 and 3 ) extending in the longitudinal direction L of the flat tube are arranged in the flat tube 2, more precisely in the central portion 20 of the flat tube 2. In the exemplary embodiment illustrated, the two corrugated bands 3 have a sinusoidal wave shape. The peaks 30 and troughs 31 have the same shape. Peaks 30 refer to those amplitudes of the corrugated bands 3 which protrude upward in the plane of the drawing; it would equally be conceivable for the amplitudes which protrude downward in the plane of the drawing to be referred to as peaks.

The corrugated bands 3 illustrated each have a constant height, and the peaks 30 and troughs 31 touch opposite inner surfaces of the flat sides 200 of the flat tubes 2. A width of the corrugated bands 3 is approximately equal to a width of the flat sides 200.

The flat tube 2 illustrated in FIG. 1 is composed of two flat tube pieces 2 a, 2 b which each extend in the longitudinal direction L. The flat tube pieces 2 a, 2 b are arranged in a mirror-symmetrical manner and are welded to one another along a weld seam 4. In the exemplary embodiment illustrated, the flat tube pieces 2 a, 2 b have at least substantially the same length. In one configuration, the flat tube pieces 2 a, 2 b are manufactured from various materials, wherein each flat tube piece 2 a, 2 b can be optimized for a temperature zone of an associated flat-tube heat exchanger. The flat tube pieces are welded to one another along a weld seam 4.

In the exemplary embodiment illustrated, a respective corrugated band 3 is provided in the flat tube pieces 2 a, 2 b, wherein the wave shape of the corrugated bands 3 is identical and the corrugated bands 3 are arranged in alignment with one another. In other configurations, the corrugated bands 3 arranged in the flat tube pieces 2 a and 2 b differ in terms of wave shape or number of waves. In yet other configurations, provision is made of a corrugated band 3 which extends beyond both flat tube pieces 2 a, 2 b.

FIGS. 4 to 6 respectively show a tube bundle space 50 of a closed housing 5 (illustrated only in part) of a flat-tube heat exchanger 1 (cf. FIGS. 7 to 10 ), which is not illustrated in FIGS. 4 to 6 , in longitudinal section, in plan view and in cross section along section line VI-VI according to FIG. 4 .

The tube bundle space 50 illustrated has a cuboid shape. A tube bundle having a plurality of flat tubes 2 according to FIG. 1 is arranged in the tube bundle space 50, a rectangular arrangement of the flat tubes 2 being provided in the exemplary embodiment illustrated. The tube bundle comprises fifty flat tubes 2, which are arranged in ten rows each comprising five flat tubes 2 which are arranged next to one another and the flat sides 200 of which lie in common planes. The number of rows and the number of flat tubes 2 per row are exemplary here, more or fewer rows are provided in other configurations. The ends 21, 22 of the flat tubes 2 are fastened in tube sheets 52.

Corrugated bands 3 as described above are arranged in the flat tubes 2, more precisely in the central portions 20 thereof (cf. FIG. 1 ). In addition, corrugated bands 6, the peaks 60 and troughs of which bear externally against the flat sides 200 of the flat tubes 2, are likewise provided between the rows of flat tubes 2. In the exemplary embodiment illustrated, the corrugated bands 6 arranged between the flat tubes 2 likewise have a sinusoidal wave shape. A height of these corrugated bands 6 corresponds at least approximately to a spacing between two rows of the flat tubes 2. In the exemplary embodiment illustrated, the corrugated bands 6 each extend over the entire row. In other configurations, two or more corrugated bands are provided per row.

As indicated schematically in FIG. 6 by way of arrows, a surface pressure is applied to the housing 5 in the region of the tube bundle space 50. The surface pressure is higher, in particular about 1 to 4 bar higher, than a pressure of the media guided in the flat tubes 2 or around the flat tubes 2. The surface pressure ensures that contact of the corrugated bands 3, 6 with the flat tubes 2 on the inner and outer sides is maintained during operation, without this requiring a materially bonded connection, in particular a welded or soldered connection, between the flat tubes 2 and the corrugated bands 3, 6. The surface pressure can be applied by a suitable apparatus.

FIGS. 7 and 8 respectively show a first exemplary embodiment of a flat-tube heat exchanger 1 having a plurality of flat tubes 2 in longitudinal section and in cross section along section line VIII-VIII according to FIG. 7 , wherein a housing 5 is surrounded by a casing housing 7 in the form of a pressure vessel.

The housing 5 comprises a tube bundle space 50, and input-side collecting space 54, an output-side collecting space 56, and two tube bundle space connections 58. The tube bundle space 50 is separated from the collecting spaces 54, 56 by means of tube sheets 52. The tube sheets 52 comprise connections for the schematically illustrated flat tubes 2, such that a medium which is supplied to the input-side collecting space 54 and which has a pressure p1 can flow from the input-side collecting space 54 into the flat tubes 2 and from the flat tubes 2 into the output-side collecting space 56.

The flat-tube heat exchanger 1 illustrated is preferably operated in counter-flow, wherein a medium which is guided around the flat tubes 2 and which has a pressure p2 is supplied via a tube bundle space connection 58, illustrated at the top in the plane of the drawing, and flows from there into the tube bundle space 50.

The casing housing 7 in the form of a pressure vessel surrounds the housing 5 with a spacing so as to leave a pressure space 70. As schematically illustrated in FIG. 8 , the casing housing 7 has a connection 72 for media supply and/or media discharge, such that a pressure p in the casing housing 7 can be regulated by media supply and/or media discharge. The pressure p in the pressure space 70 of the casing housing 7, in the form of a pressure vessel, is in this case selected in such a way that it is higher, in particular about 1 bar to about 4 bar higher, than the pressure p1, p2 of the media guided in the flat tubes 2 or around the flat tubes 2. As a result, a surface pressure is externally applied to the housing 5 and ensures that the corrugated bands 3, 6 (cf. FIGS. 1 to 6 ), which are not illustrated in FIGS. 7 and 8 , bear against the flat tubes 2 even without a materially bonded connection.

The rectangular arrangement of the flat tubes 2 illustrated in FIGS. 7 and 8 is merely exemplary. In other configurations, differing arrangements, in particular ring arrangements, of the flat tubes 2 are provided, as described in EP 2 584 201 A1. Reference is hereby made to the entire disclosure of EP 2 584 201 A1.

FIGS. 9 and 10 respectively show a second configuration of a flat-tube heat exchanger 1 having a plurality of flat tubes 2 in longitudinal section and in cross section along section line X-X according to FIG. 9 . The flat-tube heat exchanger 1 illustrated in FIGS. 9 and 10 is part of a schematically illustrated installation for thermal post-combustion (TNV), wherein contaminated air or an offgas is supplied via an input-side collecting space 54 to the flat tubes 2, and from there passes into a schematically illustrated combustion space 9. The burned offgas flows from the combustion space 9 into the tube bundle space 50, and is discharged to the surroundings via the tube bundle space connection 58. In this case, the offgas and the burned offgas usually flow in and around the flat tubes 2 only at moderate overpressure.

Corrugated bands 3, 6 (cf. FIGS. 1 to 6 ), which are not illustrated in FIGS. 9 and 10 , are arranged in the flat tubes 2 and, depending on the configuration, additionally also around the flat tubes 2, wherein an apparatus for applying a surface pressure to the housing 5 is provided, in order to ensure contact between the flat tubes and the corrugated bands 3, 6.

For this purpose, in the exemplary embodiment illustrated in FIGS. 9 and 10 , the housing 5 of the flat-tube heat exchanger 1 is also surrounded by a casing housing 7. Furthermore, provision is made of a plurality of pairs of bars, four pairs of bars 8 in the exemplary embodiment illustrated. The pairs of bars 8 each comprise two bars 80 connected by means of tie rods 82. In one configuration, spring elements are provided on the tie rods 82, said spring elements being used to brace the bars 80 with one another with a defined force. For this purpose, in other configurations, provision is alternatively or additionally made of adjusting elements, in particular adjusting screws, which can be adjusted manually or by motor. The pairs of bars 8 are used to apply a surface pressure to the casing housing 7. The application is transferred to the housing 5. For this purpose, in the exemplary embodiment illustrated, pressure rams 84, which are designed to apply a surface pressure to the housing 5 in a uniform manner, are arranged between the casing housing 7 and the housing 5.

In the exemplary embodiment illustrated, the flat tubes 2 are in a rectangular arrangement. Therefore, an application of force in a direction perpendicular to the direction of the rows of flat tubes 2 is sufficient to ensure contact between the flat tubes 2 and the corrugated bands 3 arranged therein, and also between the flat tubes 2 and the corrugated bands 6 arranged between the rows. By contrast, in the case of a flat-tube heat exchanger with a ring arrangement, provision is made of an apparatus which can be used to apply forces acting in a radial direction of the ring arrangement.

In the exemplary embodiment illustrated, thermal insulation 88 is provided between the housing 5 and the casing housing 7.

In an alternative configuration, the casing housing 7 is omitted, in which case a surface pressure is applied to the housing 5 directly by means of the pairs of bars 8.

According to the exemplary embodiments illustrated in FIGS. 1 to 6 , in each case two corrugated bands 3 having mutually aligned peaks 30 and troughs are arranged in the flat tubes 2.

FIG. 11 shows a perspective illustration of an alternative arrangement of corrugated bands 3. In the arrangement according to FIG. 11 , as viewed in a longitudinal direction L, a plurality of corrugated bands 3 having peaks 30 and troughs 31 extending in the longitudinal direction L are arranged so as to alternately run oppositely. In other words, the peaks 30 and troughs 31 of successive corrugated bands 3 are in each case phase-shifted by 180°. Transverse ribs 34 are also arranged between successive corrugated bands 3.

FIG. 12 shows a cross section of a flat tube 2 with the arrangement of corrugated bands 3 according to FIG. 11 .

Due to the alternately oppositely running arrangement of the corrugated bands 3 according to FIGS. 11 and 12 , swirling of the flow for improved heat transfer is achieved.

According to the invention, an arrangement of corrugated bands 3 in the flat tubes 2 and additionally also on outer sides of the flat tubes 2 has the effect that the size of a transfer surface for heat transfer is increased and thus the efficiency of a flat-tube heat exchanger 1 is increased. In this case, welded and/or soldered connections between the corrugated bands 3, 6 and the flat tubes 2 can be omitted, in that contact between the corrugated bands 3, 6 and the flat tubes 2 is ensured, even during operation, by application of a surface pressure to a housing 5 of the flat-tube heat exchanger 1. 

1. A flat-tube heat exchanger, in particular for gaseous media, comprising a closed housing having a tube bundle space and a tube bundle which is arranged in the tube bundle space of the housing and which comprises a plurality of flat tubes, wherein corrugated bands having peaks and troughs extending in a longitudinal direction of the flat tubes are arranged in the flat tubes and in the tube bundle space between the flat tubes, wherein the peaks and troughs bear internally or externally against flat sides of the flat tubes, and in that provision is made of an apparatus which is suitable, and configured, for externally applying a surface pressure to the housing, at least in the region of the tube bundle space said surface pressure being higher than a pressure of the media guided in the flat tubes or around the flat tubes.
 2. The flat-tube heat exchanger as claimed in claim 1, wherein a surface pressure which is about 1 bar to about 4 bar higher than a pressure of the media guided in the flat tubes or around the flat tubes is applied to the housing by means of the apparatus.
 3. The flat-tube heat exchanger as claimed in claim 1, wherein the corrugated bands have a sinusoidal, triangular or sawtooth wave shape.
 4. The flat-tube heat exchanger as claimed in claim 1, wherein a width of the corrugated bands which are arranged in the flat tubes is at least equal to a width of the flat sides of the flat tubes.
 5. The flat-tube heat exchanger as claimed in claim 1, wherein the peaks and troughs of the corrugated bands bear freely against flat sides of the flat tubes.
 6. The flat-tube heat exchanger as claimed in claim 1, wherein the apparatus comprises a casing housing which accommodates the housing, wherein the casing housing surrounds the housing, at least in the region of the tube bundle space, with a spacing so as to leave a pressure space.
 7. The flat-tube heat exchanger as claimed in claim 6, wherein the casing housing is in the form of a pressure vessel having a connection for media supply and/or media discharge, wherein a pressure in the pressure vessel can be regulated by media supply and/or media discharge.
 8. The flat-tube heat exchanger as claimed in claim 1, wherein the apparatus comprises a pair of bars and/or plates having two flexurally rigid bars or plates which are movable relative to one another and which are connected by means of tie rods, wherein at least one portion of the housing is arranged between the bars or plates of the pair of bars and/or plates.
 9. The flat-tube heat exchanger as claimed in claim 8, wherein the apparatus comprises a casing housing, wherein the casing housing surrounds the housing, at least in the region of the tube bundle space, with a spacing.
 10. The flat-tube heat exchanger as claimed in claim 9, wherein thermal insulation is provided between the casing housing and the housing.
 11. The flat-tube heat exchanger as claimed in claim 1, wherein the flat-tube heat exchanger is constructed in the form of a rectangular arrangement with a cuboid tube bundle space and with a plurality of flat tubes arranged in rows and columns.
 12. The flat-tube heat exchanger as claimed in claim 1, wherein the corrugated bands are at least partially coated with a material acting as a catalyst.
 13. The flat-tube heat exchanger as claimed in claim 1, wherein, as viewed in the longitudinal direction, in each case at least two corrugated bands are arranged so as to run oppositely in the flat tubes.
 14. The flat-tube heat exchanger as claimed in claim 13, wherein transverse ribs are arranged between two adjacent corrugated bands.
 15. The flat-tube heat exchanger as claimed in claim 1, wherein the flat tubes are each composed of at least two flat tube pieces which each extend in the longitudinal direction.
 16. The flat-tube heat exchanger as claimed in claim 9, wherein pressure rams for force transmission are arranged between the casing housing and the housing. 